Blockchain Based Hierarchical Data Storage

1. A blockchain-based hierarchical storage method comprising: generating, for a target level of storage, an empty data worksheet in response to determining that the target level of storage meets a data migration condition; storing at least a portion of a first state Merkle tree corresponding to a newly created block of a blockchain to the empty data worksheet; migrating a second state Merkle tree corresponding to a target block stored in a data worksheet to the empty data worksheet, wherein the target block has a largest block number among block numbers of blocks corresponding to state Merkle trees stored in the target level of storage; and after migrating the second state Merkle tree corresponding to the target block, migrating the state Merkle trees stored in the data worksheet to a lower level of storage than the target level of storage.

2. The method according to claim 1 , further comprising: after migrating the second state Merkle tree corresponding to the target block to the empty data worksheet, renaming the data worksheet as a historical data worksheet.

3. The method according to claim 2 , further comprising: after renaming the data worksheet as the historical data worksheet and migrating the state Merkle trees stored in the historical data worksheet to the lower level of storage, deleting the historical data worksheet.

4. The method according to claim 1 , wherein a remainder of the first state Merkle tree corresponding to the newly created block other than at least the portion of the first state Merkle tree is stored in the empty data worksheet if not all the first state Merkle tree is stored in the empty data worksheet.

5. The method according to claim 4 , further comprising: receiving a search request for a data node of the first state Merkle tree after the empty data worksheet is generated; determining whether all the first state Merkle tree is stored in the empty data worksheet; searching the empty data worksheet in response to determining that all the first state Merkle tree is stored in the empty data worksheet; and searching the empty data worksheet and the data worksheet in response to determining that not all the first state Merkle tree is stored in the empty data worksheet.

6. The method according to claim 1 , wherein the first state Merkle tree corresponding to the newly created block comprises a latest block appended to the blockchain and historical blocks migrated from higher level of storage that has higher storage cost.

7. The method according to claim 1 , wherein the blockchain is stored in a database, the database is a key-value database, data nodes included in the state Merkle state tree are stored as key-value pairs (KVPs), keys of the KVPs are hash values of corresponding values of the KVPs, and the values of the KVPs are data content of the corresponding data nodes.

8. The method according to claim 1 , wherein the first state Merkle tree or the second state Merkle tree has a tree structure constructed based on a Merkle tree and a prefix tree.

9. The method according to claim 8 , wherein the first state Merkle tree or the second state Merkle tree is a Merkle Patricia tree (MPT).

10. The method according to claim 1 , wherein the blockchain is stored in a database and the database is a LevelDB database.

11. The method according to claim 1 , wherein the blockchain is stored in a database and the database is a RocksDB database.

12. The method according to claim 1 , wherein the lower level of storage is associated with lower storage cost and lower read-write performance.

13. A computer-implemented system, comprising: one or more computers, and one or more computer memory devices interoperably coupled with the one or more computers and having tangible, non-transitory, machine-readable media storing one or more instructions that, when executed by the one or more computers, perform operations comprising: generating, for a target level of storage, an empty data worksheet in response to determining that the target level of storage meets a data migration condition; storing at least a portion of a first state Merkle tree corresponding to a newly created block of a blockchain to the empty data worksheet; migrating a second state Merkle tree corresponding to a target block stored in a data worksheet to the empty data worksheet, wherein the target block has a largest block number among block numbers of blocks corresponding to state Merkle trees stored in the target level of storage; and after migrating the second state Merkle tree corresponding to the target block, migrating the state Merkle trees stored in the data worksheet to a lower level of storage than the target level of storage.

14. The computer-implemented system according to claim 13 , further comprising: after migrating the second state Merkle tree corresponding to the target block to the empty data worksheet, renaming the data worksheet as a historical data worksheet.

15. The computer-implemented system according to claim 14 , further comprising: after renaming the data worksheet as the historical data worksheet and migrating the state Merkle trees stored in the historical data worksheet to the lower level of storage, deleting the historical data worksheet.

16. The computer-implemented system according to claim 13 , wherein a remainder of the first state Merkle tree corresponding to the newly created block other than at least the portion of the first state Merkle tree is stored in the empty data worksheet if not all the first state Merkle tree is stored in the empty data worksheet.

17. The computer-implemented system according to claim 16 , further comprising: receiving a search request for a data node of the first state Merkle tree after the empty data worksheet is generated; determining whether all the first state Merkle tree is stored in the empty data worksheet; searching the empty data worksheet in response to determining that all the first state Merkle tree is stored in the empty data worksheet; and searching the empty data worksheet and the data worksheet in response to determining that not all the first state Merkle tree is stored in the empty data worksheet.

18. The computer-implemented system according to claim 13 , wherein the first state Merkle tree corresponding to the newly created block comprises a latest block appended to the blockchain and historical blocks migrated from higher level of storage that has higher storage cost.

19. The computer-implemented system according to claim 13 , wherein the blockchain is stored in a database, the database is a key-value database, data nodes included in the state Merkle state tree are stored as key-value pairs (KVPs), keys of the KVPs are hash values of corresponding values of the KVPs, and the values of the KVPs are data content of the corresponding data nodes.

20. A non-transitory, computer-readable medium storing one or more instructions executable by a computer system to perform operations comprising: generating, for a target level of storage, an empty data worksheet in response to determining that the target level of storage meets a data migration condition; storing at least a portion of a first state Merkle tree corresponding to a newly created block of a blockchain to the empty data worksheet; migrating a second state Merkle tree corresponding to a target block stored in a data worksheet to the empty data worksheet, wherein the target block has a largest block number among block numbers of blocks corresponding to state Merkle trees stored in the target level of storage; and after migrating the second state Merkle tree corresponding to the target block, migrating the state Merkle trees stored in the data worksheet to a lower level of storage than the target level of storage.